Coated nonferrous metal and method and meterial for making the same



the surface thereof and adapted to form paint- Patented Aug 27, 1935 UNITED, STATES COATED NONFERROUSMETAL AND METH- OD AND MATERIAL FOR MAKING THE SAME Robert R. Tanner, Highland Park, and Herman J. Lodeesen, Detroit, Mich., assignors to Metal Finishing Research Corporation, Detroit, Mich., a corporation of Michigan No Drawing. Application July 14, 1932,

Serial No. 622,454

' 16 Claims. (Cl. 148-6) This application relates to the coating ofnonferrous metals, particularly lead, tin, cadmium and alloys thereof, with substantially integral coatings of salts of the'metal formed in situ on holding coats.

More particularly the application relates to coated lead, tin, cadmium or their alloys having coatings formed by the action of a solution of an organic acid with a suitable accelerator or accelerators.

In a co-pending application of applicant, Robert R. Tanner, there is disclosed and claimed a method of coating iron, zinc, or their alloys, with an organic acid, an accelerator being employed preferably, although not necessarily, with certain of the acids. The organic acids found suitable for this purpose comprise the dicarboxylic and hydroxy-dicarboxylic acids of the aliphatic series and carboxylic, phenolic-carboxylic and sulphonic acids of the aromatic series, the useful carboxylic acids of the aromatic series being chiefly the mono-carboxylic acids. None of these acids alone has been found to produce a paint-holding coat on a panel of lead, or of tin. Applicants have discovered, however,'that these metals and their alloys can be coated by acids of the above list when properly accelerated. Applicants have further discovered that cadmium can be coated by the same acids.

The most important of the acids within the list above indicated are oxalic, malonic, succinic, glutaric, adipic, malic, tartaric, benzoic, salicylic, gallic, tannic, benzene-sulphonic and similar sulphonic acids. The accelerators suitable or necessary for producing the desired coats may be divided into two classes, first, those comprising soluble compounds containing a metal and, second, those comprising oxidizing agents.

Of the first class, compounds containing copper are the most universally effective and easily obtained. In addition, antimony, silver, mercury, molybdenum and uranium and other metals below lead in the electro-motive series, with the exception of arsenic, bismuth and tungsten, act as accelerators for coating tin and lead. In additionto these, zinc, nickel, tin and lead all act as accelerators, in an oxalate bath, for example, for coating cadmium.

Amongst the oxidizing agents, the nitrates are agents on-the border line,

the most practical large class to be generally effective. In order to act as an accelerator, the oxidizing agent must be capable of oxidizing hydrogen as it is released by the action of the solution on the metal, and to do this, it must not ex- 5 haust its oxidizing power in oxidizing the acid. For example, potassium permanganate in an oxalic acid solution exhausts itself so rapidly in oxidizing the acid that it merely uses up the acid without accelerating the action of the solution. Other strong oxidizing agents act in the same way. Manganese dioxide is on the border line. It is reduced by oxalic acid, but it introduces manganese into the solution which generally helps some. The manganese introduced by potassium permanganate does not offset the detrimental effect of its action upon the acid.

Hydrogen peroxide is not reduced by oxalic acid rapidly below a temperature of 150 F. Above that temperature the beneficial effect is lost by the action of the oxidizing agent upon the oxalic acid.

The nitrates act as accelerators in the oxalic acid bath up to a temperature about 185 F., above which they oxidize the acid and lose their ef- I fectiveness.

To summarize, the test of the desirability of an oxidizing agent with a given solution is whether or not it exhausts itself and the acid, in oxidizing theacid or being reduced by the acid. This may be testedfor carboxylic acids by introducing the oxidizing agent into a solution of the acid-and observing whether or notCOz gas escapes. If it does, the oxidizing agent is exhausting itself and the acid. If this formation of CO2 gas'is rapid, the oxidizing agent is a detriment rather than a benefit. If no escapeof CO2 gas is observed, the oxidizing agent comes within the desirable class. If there is some slow formation of CO2 gas, the agent may be helpful, but with the oxidizing 40 care must be taken to keep the solution below the temperature where the effectiveness of the oxidizing agent will be lost.

Another way of testing the action of the oxidizing agent upon the acid wouldbe to test the acidity of the solution with a standard alkali before and after introducing the oxidizing agent.

While the principles stated above apply-generally to tin, lead, cadmium and their alloys, there 50 are certain features in which the different metals 5 tin alone by any On terne plate, in particular, the

. by an oxalic acid solution is noticeably harder when a copper compound plus a nitrate is employed, than where a copper compound is employed alone. While this appears to be a general rule with the solutions of oxalic, malonic, glutaric, malic and salicylic acids, and is true of all the acids tested, when coating cadmium, there are some exceptions when coating tin, lead and terne plate.

For example, solutions of tannic or benzenesulphonic acids produce better coatings on tin .when accelerated by both a copper compound and an oxidizing agent than when accelerated by the copper compound alone, while these acids produce a better coating on lead and terne plate when accelerated by a copper compound alone than when accelerated by both a copper compound and an oxidizing agent. On the other hand, the use of both a copper compound and an coating action benzoic acids oxidizing agent results in a better of succinic, adipic, tartaric and upon lead or terne plate than the use of the-cop-.

per compound alone, while with these same acids a better coating is produced on tin when a copper compound is used alone as an accelerator than when both the copper compound and an oxidizing agent are used. A solution of gallic acid, containing the copper accelerator alone, is superior in treating either tin or lead to the same solution with sodium nitrate added, but on terne plate not much diiference was observed. It is diillcult to coat lead with a solution of malic acid, and the addition of a copper compound and/or sodium nitrate, in proportions which render most of the other solutions readily operative, does not produce any satisfactory coat on lead. However, malic acid can be made to coat lead by employing a compound of mercury with sodium nitrate as accelerators. In this connection, it may be stated that mercury is deposited more readily and quickly than copper and, therefore, has a greater accelerating action where it is dimcult to produce a coat withoutconsiderable acceleration. n the other hand, where the other accelerators are satisfactory, the use of mercury must be very carefully controlled in order to avoid excessive deposition and a smudgy coat.

For most commercial purposes, the most important acid of the seriesis oxalic acid, since that is as active as anyin producing a coat and is the cheapest and, most readily obtainable, and for most purposes requires less careful manipulation than the other acids.

There maybeconsiderable variation in the concentration of the solutions but, in general, 15 gramsof the acid per 100 cc. of watenforms a satisfactory strength. A convenient way 01 adding a copper compound as an accelerator is to dissolve 5 grams copper sulphate in 100 cc. of

water; andadd suincient of this solution to ob-- tain thid'esired results. In general, 2 cc. of the copper sulphate solution added to 100 cc. of the acid solution is sufllcient for the metallic accelwhere the metal accelerator is omitted, it'has been found desirable to add as much as grams of sodium nitrate to the solution to obtain a satisfactory coating on tin. In general, the coating can be rendered harder by increasing the oxidizing agent. As previously noted, this does 'not work out satisfactorily where a metallic accelerator is used also, and where tin is being coated with succinic, adipic, tartaric, benzoic or gallic acid, or where lead is'being coated with gallic, tannic or benzene-sulphonic acids.

In solutions such as indicated above, sodium nitrite is more efiective than'sodium nitrate in amounts under 'about'15 grams per 100 cc. of solution, but in larger amounts the nitrate is preferable.

The amount of metal compound desirable or permissible as an accelerator, varies widely with the surface being coated, the kind and strength of the acid used, the kind of metal accelerator used, andthe kind and amount of oxidizing agent employed. In general, it may be stated that the accelerating metal is deposited as metal interspersed throughthe saltcoating, and too great a proportion of the metal in the coating renders it smudgy. The amount of metal in the coating depends upon the relative speeds of deposition of the'metal and formation of the salt coat. The

Silver and mercury are deposited more rapidly than copper, under similar conditions and, therefore, silver or mercury should be used in less quantities than copper in an otherwise similar solution. Antimony, molybdenum and uranium may be used in larger quantities than can copper in a given solution. a

It will be recognized that the above outlined principles may be followed to compound a wide variety of solutions by use of the various ingredients in different proportions. Oxalic acid is more active thanv many of the acids which it is possible to use, and is preferably employed in greater dilution. One formula which gives good results for commercial treatment of terne plate is 40 gals. of water, 5 lbs. of oxalic acid, lbs. of sodium nitrate and y, oz. copper sulphate. It will be-understood that this is given by way of example only.

In general, it is more difli'cult to coat tin and lead than it is to coat iron and zinc, as will be seen from comparing the disclosure in the (to-pending application previously mentioned; but tannic acid and the accelerating compounds of mercury antimony, molybdenum and uranium are more eflcctive in coating lead or tin than in coating irm or zinc.

The proportion of 'coatable metal. which is necessary in an alloy in order to make the alloy-receive the coat properly, varies considerablywith different combinations of metal. in general,

ing of zinc, nickel, tin,

' the most easily coatable where two or more coatable metals are included in the alloy, the coating operation is fully as easy and satisfactory on the alloy as it would be upon of the two metals. It is not always necessary to have as much as 50% of a coatable metal in the alloy in order to make the alloy receive a coating. This is particularly true with aluminum alloys, since an aluminum alloy containing much less than 50% of coatable metals may be readily co ted by solutions, such as outlined above, althoug the pure aluminum is not coated by these solutions. Therefore in the appended claims, where metals and their alloys are claimed, it is to be understood that the term alloys is intended to cover any metal composition containing enough of the coatable metal to enable the alloy to receive the coating, even' though there may be less than 50%.

What we claim is:- 1. An article having a surface of metal, of the class consisting of lead, tin, and cadmium and alloys thereof, coated with a coating the major portion of which is, a salt formed in situthereon, the

base of the salt being of the metal that is coated and the acid radical being one of the group consisting of the dicarboxylic and hydroxy-di'carboxylic acids of the aliphatic series and the car-.

boxylic, phenolic carboxylic, and sulphonic acids of the aromatic series.

2. An article in accordance with claim 1, and in which the coating contains, interspersed through the salt coating, particles of a metal of the group comprising copper, silver, mercury, antimony, molybdenum, and uranium.

3. An article in accordance with claim 1, and having the metal surface of cadmium and the coating containing a metal of the group consistlead, antimony, molybdenum, uranium, copper, silver and mercury.

4. The method of coating a surface of a metal, of the group consisting of lead, tin, cadmium and their alloys, which-consists in treating said surface with a solution containing, as its chief coating chemical, an acid, of the group consisting of the dicarboxylic and hydroxy-dicarboxylic acids of the aliphatic series and the carboxylic, phenolic-carboxylic and sulphonic acids of the aromatic series, and an accelerating agent of the group consisting of soluble compounds of metals. of the group consisting of copper, silver, mercury, molybdenum, antimony, and uranium and soluble oxidizing agents which are not reduced by the acid in the solution, regulating the amount of any accelerated soluble compound of metal in the solution, inversely as to the free acidity of'the solution and directly as to the rate of formation of a salt coating by the solution, so as to expedite the formation on the metal to be coated of a difllcultly soluble salt of the metal being coated and the acid being employed, without depositing moremetal from the solution than is interspersed through and imbedded in the salt coating, and continuing the treatment of the surface with the solution until a coating is formed suitable for bonding paint to the surface.

. 5. Amethod in accordance with claim 4, and in which the accelerating agent comprises a soluble compound of copper.

6. A method in accordance with claim'4, and in which the accelerator comprises a soluble compound of mercury.

'1. A method in accordance with claim 4, and in I which the accelerator comprises a soluble compound of molybdenum.

8. A method in accordance with claim 4, and in which the accelerator comprises a nitrate.

9. A method in accordance with claim 4, and in which the acid comprises oxalic acid, the accelerating agent comprises a nitrate, and in which the temperature is kept below F.

10. A. method in accordance with claim 4, and

in which the accelerating agent comprises both a soluble compound of a metal and an oxidizing agent.

11. A method in accordance with claim 4, and in which the acid employed is of the group consisting of oxalic, malonic, glutaric, malic and salicylic acids, and the accelerator comprises both a soluble compound of a metal and an oxidizing agent.

12. A method in accordance with claim 4, and in which the acid employed is of the group consisting of tannic and benzene-sulphonic'acids, the metal surface treated comprises tin, and the accelerator comprises both a soluble compound of a metal and an oxidizing agent.

13. A method in accordance with claim 4, and in which the metal treated comprises lead, the acid used is of the group consisting of succinic, adipic, tartaric and benzoic, and the accelerator comprises both a soluble compound of a metal and i an oxidizing agent.

, 14. A material for coating metal, comprising an aqueous solution of an acid of the group consisting of carboxylic and hydroxydicarboxyli'c acids of the aliphatic series and carboxylic, phenolic-carboxylic, and sulphonic acids of the aromatic series, 'said solution containing as an accelerator a soluble compound of a metal of the group consisting of mercury, molydenum and uranium. a

15; A material in accordance with claim 14, and in which the soluble accelerating compound is of mercury.

16. A material in accordance with claim 14,

and in which the soluble accelerating compound is of molybdenum.

ROBERT R. TANNER. HERMAN J. LODEESEN. 

